Continuous strand sintering is used, after pelletizing powdery mineral material, for agglomerating pellets, which improves the strength and reactivity of the pellets. In this specification, the term ‘mineral material’ refers to a mineral that has similar crystal chemistry properties as those of the oxide group and contains the metal to be recovered, the metal being mainly present as compounds of metal and oxygen.
A strand sintering furnace is divided into several sequential zones, with different temperature conditions prevailing in each one of them. The strand sintering equipment includes a perforated conveyor belt, which is conveyed as an endless loop around two deflector rolls. At the forward end of the furnace, wet fresh pellets are fed onto the conveyor belt to form a bed with a thickness of a few decimeters. The conveyor belt conveys the bed of pellets through the drying, heating, sintering and equalizing zones of the sintering furnace, and further through sequential cooling zones. The cooling zones comprise cooling chambers that are separated by partition walls. After traveling through the cooling zones, the pellets are discharged at the tail end of the strand sintering equipment in a sintered form. To optimize the energy economy, the energy contained in the cooling gases at the tail end of the furnace is used for drying, heating and sintering at the forward end of the furnace, wherefore the strand sintering equipment includes overhead circulation gas ducts for realizing the gas circulation mentioned above. Burners are placed in the circulation gas ducts, and they are used to increase the temperature of the conducted gas up to the sintering temperature required in the sintering process. Below the conveyor belt, there are provided lower exhaust gas ducts for conducting out, through washers, the gas that exits each drying/heating/sintering zone, and has been conducted through the pellet bed and the conveyor belt. Below the conveyor belt, there are arranged lower inlet gas ducts for conducting the gas to the cooling zones. The movement of the gas in the ducts is provided by means of blowers, which are arranged in the lower exhaust and inlet gas ducts.
In a known strand sintering furnace, the partition wall between the sequential adjacent cooling chambers is placed so near to the surface of the pellet bed that any gas exchange cannot essentially take place in between the cooling chambers. Therefore the pressure prevailing in adjacent cooling chambers can be different, when a different quantity of gas is sucked from a certain cooling chamber than what is blown in from below. The drawback is that the gas quantity to be blown in from below must be accurately adjusted at each cooling chamber separately. Yet another drawback is that for each cooling chamber, it has been necessary to provide a specific blower. A large quantity of blowers in turn makes the equipment expensive.